Silage grown as feedstock for anaerobic digestion (AD) plants is more valuable than ever as crop yields are reduced due to the recent hot dry weather, and input and contractor costs have increased.
The Met Office reports that England had just 35% (23.1mm) of its average rainfall in July 2022, with the south and east of the country being especially dry.
The exceptionally dry, hot weather seen in June and July has particularly affected maize crops, which have reacted to the stressful conditions by flowering much earlier than normal in mid-July. Early flowering crops will yield much less than average.
Other wholecrop cereals such as rye have also yielded much lower than normal in many areas. “In some places, growers have reported disappointing yields, while others have decided to combine crops due to high commodity prices. Overall, this means there is less wholecrop silage available for AD and some plants are already running out of feedstock,” comments Andy Lee, national biogas silage specialist at FM BioEnergy.
Additionally, eyespot (Aureobasidium zeae), which is becoming more problematic due to increased levels of maize production across the country. “Maize eyespot overwinters in the soil and affects the leaves, so it has the potential to greatly reduce overall yields,” says Lee. “It favours humid conditions and some growers in the west of the country, which has received more rainfall than other places, have had to spray to control the disease, as left untreated it can reduce yields by 25-50%.”
FM Bioenergy predicts a strong demand for its feedstock supply services in the coming season and is urging plant operators who may need help with feedstock procurement to make contact sooner rather than later.
Typical fermentation losses of untreated silage can be reduced from 10% to 3% by adding a suitable silage treatment, such as FM BioEnergy’s Silasil Energy XD. However, losses due to aerobic spoilage caused by organisms such as yeasts, can be another 5-10%.
“In a worst-case scenario growers could lose almost a fifth of their silage, which is why treatment is so important,” stresses Lee. “With climate change and warmer winters, we are seeing a lot more yeasts around. In some cases, we have counts of 12 million CFU/gFM on treated crops, so the potential for aerobic losses in the clamp is enormous.”
Lee explains that not all silage additives and treatments are the same. Many of the treatments which are originally designed for use by livestock farmers will reduce fermentation losses, but they do not produce acetic acid, and therefore do not prevent aerobic losses.
Lee adds that growers should pay attention to temperature: “I recently looked at a freshly cut clamp of wholecrop rye. After just six hours the temperature at the face had increased by 20°C. If you think about the amount of silage crops that are water-based, and the energy needed to heat water by 20 °C, you can see how much energy is being lost as the aerobic organisms get to work digesting the valuable carbohydrates.”
“Acetic acid is probably the best natural anti-fungal there is and is excellent at controlling yeasts before they have a chance to multiply,” he explains. “As the only biogas silage additive independently approved by the DLG (the German Agricultural Society) for increased methane yield and improved aerobic stability, Silasil Energy XD contains a new strain with unique metabolism that produces acetic acid very quickly – clamps can be opened in as little as two weeks compared to eight weeks for a typical livestock additive.
“With the hot dry weather showing no sign of abating, growers would be well advised to protect their silage and preserve their biogas output.”